Job complexity and employee intelligence covary strongly. Likewise, race differences exist on mean IQ / g scores. Spearman’s hypothesis predicts that race differences on cognitive tests are mainly g differences, and that the former should covary with how well mental tests measure the latter. Here we use jobs as “mental tests,” and predict that as job IQ increases, the percent of White and Asian workers will increase, while the percent of Black workers will decrease. We found moderate to strong support for Spearman’s hypothesis across these three racial groups. We also found a very large correlation (.86) between job IQ and complexity, as measured by the U.S. Federal Government’s Dictionary of Occupational Titles classification scheme. In sum, like different mental tests, different jobs are more or less g-loaded. And, consistent with Spearman’s hypothesis, the g-loading of a job predicts its demographic composition.